Method of detecting elevator tab failure

ABSTRACT

A method is provided for verifying proper operation of a left elevator tab disposed at an end portion of a left elevator of an aircraft and a right elevator tab disposed at an end portion of a right elevator of the aircraft. Because proper operation of the elevator tabs cannot be directly verified by existing aircraft instrument, the operation of the elevator tabs can be indirectly verified by analyzing flight data of the aircraft. After identification of a verification event, in which the elevator tabs move relative to the elevators, the positions of the left elevator and right elevator can be measured, and differences in the positions of the left elevator and right elevator can indicate proper operation of the left and right elevator tabs.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.15/099,547, entitled “Method of Detecting Elevator Tab Failure” andfiled Apr. 14, 2016, which is incorporated herein by reference in itsentirety.

FIELD OF THE DISCLOSURE

This disclosure relates generally to detecting a latent fault in anaircraft control system, and in particular, to detecting a fault in theoperation of elevator tabs used with an aircraft's elevator.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

The “Next Generation” 737 (the “737NG”) was designed to fly higher,faster, carry heavier loads, and be more fuel efficient than itspredecessor, the 737 Classic, which is manufactured by the BoeingCompany. However, airlines flying the 737 Classic at the time of theplanned upgrade wanted to limit changes to specific features of the 737Classic to control costs associated with the upgrade. Specifically, theairlines wanted the 737NG to have the same type rating as the 737Classic so that 737 Classic pilots would not need costly recertificationto fly the 737NG. In addition, the airlines wanted the 737NG to have thesame basic design and same airframe as the 737 Classic to utilize thesame mechanics, tooling, and spare parts as the 737 Classic.

In accordance with this direction, the 737NG has the same—or nearly thesame—airframe, wing area, and control surfaces as the 737 Classic, andthe size of the 737 Classic elevators (a control surface on thehorizontal tail wings of an aircraft that control pitch) were notchanged on the larger and heavier 737NG. However, the 737NG has morepowerful engines and higher gross weights than the 737 Classic, and the737NG therefore requires more aerodynamic authority then the existing737 Classic elevators were capable of developing. Consequently, withreference FIG. 2, engineers developed dual-functioning elevator tabs 10a, 10 b that are disposed or positioned adjacent to a trailing edge ofeach elevator 12 a, 12 b on each horizontal stabilizer 14 a, 14 b of the737NG and that are displaceable relative to the respective elevator 12a, 12 b. During normal flight operations, the elevator tabs 10 a, 10 bmay function in a “balance” mode (illustrated in FIGS. 4B and 4D) as aportion of the elevators 12 a, 12 b. However, the elevator tabs 10 a, 10b are automatically reversed to an “anti-balance” function (illustratedin FIGS. 4A and 4C) to displace relative to each corresponding elevator12 a, 12 b in two specific flight conditions: (1) hydraulics engaged;and (2) flaps not retracted.

The “balance” function of the elevator tabs 12 a, 12 b relates to theredundant flight control functions of the 737NG. The 737NG has twoprimary hydraulic systems, but the 737NG is capable of operating withone or even both of those hydraulic systems failed. In the case of dualfailure of the hydraulic systems, the pilot can still control the 737NGby physical strength combined with the help of aerodynamic andmechanical devices and couplings. In such a scenario, and as illustratedin FIGS. 4B and 4D, the “balance” function of the elevator tabs 10 a, 10b displaces the elevator tabs 10 a, 10 b in opposition to displacementof the elevators 12 a, 12 b. That is, when the elevator 12 a, 12 b(i.e., a trailing edge 28 a, 28 b of each elevator) pivots upwardly (asillustrated in FIG. 4B), the corresponding elevator tab 10 a, 10 b(i.e., the trailing edge of the elevator tabs 10 a, 10 b) pivotsdownwardly, and when the elevator 12 a, 12 b pivots downwardly (asillustrated in FIG. 4D), the corresponding elevator tab 10 a, 10 bpivots upwardly. This opposition movement applies an assisting load tothe elevator surface allowing the pilot to move the elevator 12 a, 12 bwhen operating without hydraulic power. If the “balance” function of theelevator tabs 10 a, 10 b was to fail when required, the 737NG could notbe manually controlled by a pilot.

A second elevator tab engagement scenario involves a takeoff from arunway with a limited length when an engine fails just after theaircraft has achieved V₁ speed (the speed reached during takeoff whereit is just possible to stop the aircraft with the remaining distance ofrunway). If V₁ speed is exceeded, the aircraft is required to completethe takeoff or it will overrun the remaining runway if the takeoff isaborted. In such a takeoff, the elevator tabs 10 a, 10 b perform an“anti-balance” function in which the elevator tabs 10 a, 10 b displacein concert with the elevators 12 a, 12 b. That is, when the elevator 12a, 12 b (i.e., the trailing edge of the elevator 12 a, 12 b) pivotsupwardly, the corresponding elevator tab 10 a, 10 b (i.e., the trailingedge of the elevator tabs 10 a, 10 b) pivots upwardly (as illustrated inFIG. 4A), and when the elevator 12 a, 12 b pivots downwardly, thecorresponding elevator tab 10 a, 10 b pivots downwardly (as illustratedin FIG. 4C). This in-concert displacement movement generates a greaterelevator surface hinge moment than the elevator of a 737 Classic,thereby allowing the elevators 12 a, 12 b and elevator tabs 10 a, 10 bto rotate the aircraft before reaching the end of that runway. As withthe “balance” function, if the “anti-balance” function was to fail whenrequired, the aircraft would not have sufficient control authority to beassured of maintaining safe, continued flight.

While the elevator tabs perform a critical function in the two scenariosdescribed above, the operation of the elevator tabs is entirelycontrolled by computer, and the pilots have no ability to manually orspecifically control their operation. In addition, because the elevatortabs are not a part native to the 737 Classic, no instrumentation isconnected to or in communication with the elevator tabs to directlydetect failures, and the pilot (and flight computer) has no indicationthat the elevator tabs are functioning (or can function) properly.Accordingly, there is a need for a method or system to indirectly detectproper operation of the elevator tabs to ensure that the “balance” or“anti-balance” functions are available in an emergency.

BRIEF SUMMARY OF THE DISCLOSURE

Techniques are provided for assessing and verifying proper operation ofa left elevator tab disposed at an end portion of a left elevator of anaircraft and a right elevator tab disposed at an end portion of a rightelevator of the aircraft. The techniques include determining theoccurrence of a verification event that includes movement of the leftelevator tab relative to the left elevator and the right elevator tabrelative to the right elevator, wherein the verification event occurs ata start time, wherein the left elevator is at an initial rotationalposition and the right elevator is at an initial rotational position atthe start time. The techniques also include determining a firstrotational position of the left elevator at a first time and a firstrotational position of the right elevator at the first time, and thefirst time occurs after the start time. The first rotational position ofthe left elevator at the first time is compared to the first rotationalposition of the right elevator at the first time. If the firstrotational position of the left elevator at the first time is notdifferent than the first rotational position of the right elevator atthe first time by at least a first value, a first alert is issuedassociated with the left elevator tab.

A second rotational position of the left elevator at a second time and asecond rotational position of the right elevator at the second time aredetermined, and the second time occurs after the first time. Thedifference between the start time and the second time is equal to anintentional delay between functionality of the left elevator tab and theright elevator tab. The second rotational position of the left elevatorat the second time is compared to the second rotational position of theright elevator at the elevator at the first time. If the secondrotational position of the right elevator at the second time is notwithin a second range of the second rotational position of the leftelevator at the second time, a second alert is issued associated withthe right elevator tab. If (a) the second rotational position of theleft elevator at the second time is within a third range of the initialrotational position of the left elevator at the start time and (b) thesecond rotational position of the right elevator at the second time iswithin the third range of the initial rotational position of the rightelevator at the start time, a third alert is issued associated with boththe left elevator tab and the right elevator tab.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of the method forverifying proper operation of a left elevator tab disposed at an endportion of a left elevator of an aircraft and a right elevator tabdisposed at an end portion of a right elevator of the aircraft;

FIG. 2 is a partial plan view of a rear portion of an aircraft showingthe horizontal stabilizers;

FIG. 3A is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 3B is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 3C is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 4A is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 4B is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 4C is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 4D is sectional view taken along line A-A and B-B of FIG. 2;

FIG. 5A is partial sectional view taken along line A-A and B-B of FIG.2;

FIG. 5B is partial sectional view taken along line A-A and B-B of FIG.2;

FIGS. 6A to 6C are partial sectional views taken along line A-A of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 6D to 6F are partial sectional views taken along line B-B of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 7A to 7C are partial sectional views taken along line A-A of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 7D to 7F are partial sectional views taken along line B-B of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 8A to 8C are partial sectional views taken along line A-A of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 8D to 8F are partial sectional views taken along line B-B of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 9A to 9C are partial sectional views taken along line A-A of FIG.2 at a start time, a first time, and a second time, respectively;

FIGS. 9D to 9F are partial sectional views taken along line B-B of FIG.2 at a start time, a first time, and a second time, respectively;

FIG. 10 is a schematic view of a system for assessing and verifyingproper elevator tab operation in aircraft; and

FIG. 11 is a schematic view of modules of a process of the system of theembodiment of FIG. 10.

DETAILED DESCRIPTION

As illustrated schematically in FIG. 1, a method is provided forverifying proper operation of a first elevator tab (such as a leftelevator tab) disposed at an end portion of a first elevator (such as aleft elevator) of an aircraft and a second elevator tab (such as a rightelevator tab) disposed at an end portion of a second elevator (such as aright elevator) of the aircraft. The provided method utilizes anintentional delay (e.g., a ten-second time delay) between the functionof the left elevator tab and the subsequent function of the rightelevator tab when the flaps are first extended. The techniques hereinmay be implemented by a flight diagnostic system such as that providedin FIG. 10 (discussed below). The techniques analyze flight data of theaircraft after one or more flights have been completed. The analysisinvolves automatic identification of a verification event, which may bethe operation of the horizontal stabilizers of an aircraft and includesmovement of the left elevator tab relative to the left elevator and theright elevator tab relative to the right elevator, wherein theverification event occurs at a start time. In an example, at the startof the verification event, the left elevator tab moves relative to theleft elevator. However, due to the intentional delay, the right elevatortab does not move relative to the right elevator. Because the deploymentof the left elevator tab relative to the left elevator createsaerodynamic forces, the left elevator immediately displaces relative toits position at or just prior to the initiation of the verificationevent. By contrast, the right elevator does not displace immediatelyafter the initiation of the verification. Accordingly, by analyzingflight data, the diagnostic system can infer or detect a displacement ofthe left elevator tab following a verification event, by confirming thatthe left elevator immediately displaced (relative to both or either ofits initial position or to the right elevator).

While examples herein are described in reference to movement of the leftelevator tab preceding that of the right elevator tab, it is noted thatthe converse ordering may be implemented with the same results. Theexamples are described with the left elevator tab leading, because thatcorresponds to the present operation specifications of certain exampleaircraft.

At the expiration of the intentional delay, the right elevator tabdisplaces relative to the right elevator, and this displacement createsaerodynamic forces on the right elevator that immediately displaces theright elevator relative to its position at or just prior to theexpiration of the intentional delay. By analyzing flight data, adisplacement of the right elevator tab can be inferred or detectedfollowing the expiration of the intentional delay by confirming that theright elevator immediately displaced (relative to both or either of itsinitial position or to the left elevator). The techniques thereforeallow the proper operation of the left elevator tab and the rightelevator tab to be indirectly verified by data analysis of existingflight parameters, thereby avoiding the installation of costly newsensors, parts, and instrumentation.

In an example implementation, available flight data (such as, forexample, data from a Digital Flight Data Recorder (“DFDR”) or a quickaccess recorder (“QAR”)) is automatically analyzed by a diagnosticsystem (e.g., FIG. 10) that employs an elevator tab comparison algorithmto determine if a verification event has occurred during a flight of theaircraft. In response to triggering by a verification event, which maybe an operation that involves movement of the left elevator tab 10 a(see FIG. 2) relative to the left elevator 12 a of the horizontalstabilizer 14 and the right elevator tab 10 b relative to the rightelevator 12 b of the horizontal stabilizers, the system performs theassessment and verification. The diagnostic system, which may operate onhistorical available flight data or in real time on collected flightdata, can identify a verification event typically on each flight.Because the operation of the elevator tabs 10 a, 10 b cannot be directlycontrolled (or monitored) by the pilot, the verification event is anoperation of the elevators 12 a, 12 b that automatically involves therotational displacement of the left and right elevator tabs 10 a, 10 brelative to the left and right elevators 12 a, 12 b, respectively. Anexample of a verification event may be, for example, a flight operation,such as moving the aircraft's flap control lever out of the “up” detentor disengaging either or both of the aircraft's redundant hydraulicsystems that operate the left and right elevators 12 a, 12 b. A furtherexample of a verification event may be a failure of one or both of theredundant hydraulic systems.

The verification event occurs at a start time, and at this start timeand/or immediately prior to this start time (e.g., 0.5 to 0.25 secondsbefore), the left elevator 12 a is at an initial rotational position andthe right elevator 12 b is at an initial rotational position. This andall positional and time information relating the left and right elevatortabs 10 a, 10 b and the left and right elevators 12 a, 12 b is stored asflight data (see, for example, stored flight data 216 of FIG. 10).However, the flight data may be real-time data (or may in part bereal-time data) that may be available to the controller 204 and/orstored the memory 206 of FIG. 10. The occurrence of the verificationevent at the start time may be determined, for example, by the computersystem 200 of FIG. 10, which will be described in more detail below. Thecomputer system 200 may be particularly configured to automaticallyaccess stored flight data (e.g., over a communication network), wheresuch access may be performed on a periodic basis determined by aschedule or based on a number of flights since the last analysis or someother event. In some examples, the computer system 200 accesses flightdata based on a triggering event, whether in real-time during flight orafter a flight. The computer system 200 may automatically search for theverification event data stored in the flight data and from there beginanalysis and verification.

An example of an initial rotational position of the left elevator 12 ais provided in FIG. 3A, which illustrates that a longitudinal axis 16 aof the left elevator 12 a is aligned (e.g., collinearly aligned) with alongitudinal axis 18 a of the left elevator tab 10 a. The longitudinalaxis 16 a of the left elevator 12 a and the longitudinal axis 18 a ofthe left elevator tab 10 a may extend across the length of the leftelevator tab 10 a and the left elevator 12 a, respectively along thesectional line A-A of FIG. 2. In some embodiments, the longitudinal axis16 a of the left elevator 12 a and the longitudinal axis 18 a of theleft elevator tab 10 a may bisect or substantially bisect the leftelevator tab 10 a and the left elevator 12 a, respectively along thesectional line A-A of FIG. 2.

At (and/or just prior to) the start time, the left elevator tab 10 a andthe left elevator 12 a act as a single control surface that rotates as aunit relative to a portion of the left horizontal stabilizer 14 a abouta left elevator rotational point 20 a, as illustrated in FIG. 3A. Thus,at the initial rotational position of the left elevator 12 a, thelongitudinal axis 16 a of the left elevator 12 a and the longitudinalaxis 18 a of the left elevator tab 10 a may be aligned with alongitudinal axis 22 a of the left horizontal stabilizer 14 a, asillustrated in FIG. 3A. In addition, the longitudinal axis 16 a of theleft elevator 12 a and the longitudinal axis 18 a of the left elevatortab 10 a may form an acute angle (either clockwise or counterclockwise)with the longitudinal axis 22 a of the left horizontal stabilizer 14 a,as illustrated in FIGS. 3B and 3C.

Also at the start time and/or immediately prior to this start time(e.g., 0.5 to 0.25 seconds before), the right elevator 12 b is at aninitial rotational position and the right elevator 12 b is at an initialrotational position. An example of an initial rotational position of theright elevator 12 b is provided in FIG. 3A, which illustrates that alongitudinal axis 16 b of the right elevator 12 b is aligned (e.g.,collinearly aligned) with a longitudinal axis 18 b of the right elevatortab 10 b. The longitudinal axis 16 b of the right elevator 12 b and thelongitudinal axis 18 b of the right elevator tab 10 b may extend acrossthe length of the right elevator tab 10 b and the right elevator 12 b,respectively along the sectional line B-B of FIG. 2. In someembodiments, the longitudinal axis 16 b of the right elevator 12 b andthe longitudinal axis 18 b of the right elevator tab 10 b may bisect orsubstantially bisect the right elevator tab 10 b and the right elevator12 b, respectively along the sectional line B-B of FIG. 2.

At (and/or just prior to) the start time, the right elevator tab 10 band the right elevator 12 b act as a single control surface that rotatesas a unit relative to a portion of the right horizontal stabilizer 14 babout a right elevator rotational point 20 b, as illustrated in FIG. 3A.Thus, at the initial rotational position of the right elevator 12 b, thelongitudinal axis 16 b of the right elevator 12 b and the longitudinalaxis 18 b of the right elevator tab 10 b may be aligned with alongitudinal axis 22 a of the right horizontal stabilizer 14 b, asillustrated in FIG. 3A. In addition, the longitudinal axis 16 b of theright elevator 12 b and the longitudinal axis 18 b of the right elevatortab 10 b may form an acute angle (either clockwise or counterclockwise)with the longitudinal axis 22 b of the right horizontal stabilizer 14 b,as illustrated in FIGS. 3B and 3C.

At a first time, which occurs immediately or nearly immediately afterthe verification event, the left elevator tab 10 a rotates relative tothe left elevator 12 a, while due to the intentional delay, the rightelevator tab 10 b does not rotate or displace relative to the rightelevator 12 b. The first time may occur after the start time but beforethe intentional delay expires, and the first time may be any length oftime that allows a displacement (i.e., a statistically significantrotational displacement) of the left elevator 12 a relative to the rightelevator 12 b to be detected by analyzing flight data. For example, thefirst time may occur between 0.0 to 1.0 second after the start time.

The left elevator tab 10 a may rotatably displace in one of twodirections relative to the left elevator 12 (or relative to a point onthe left elevator). As illustrated in FIG. 5A (in which the lefthorizontal stabilizer 14 a is eliminated for clarity), the left elevatortab 10 a may rotate counter-clockwise about a left tab rotation point 24a that is disposed at or adjacent to a leading edge 26 a of the leftelevator tab 10 a (and/or at or adjacent to a trailing edge 28 a of theleft elevator 12 a). Such a counter-clockwise rotation of the leftelevator tab 10 a is involved in the “balance” function of the leftelevator tab 10 a when the left elevator 12 a rotates clockwise relativeto the left elevator 12 a (or clockwise about the left elevatorrotational point 20 a), as illustrated in FIG. 4D. In addition, acounter-clockwise rotation of the left elevator tab 10 a is involved inthe “anti-balance” function of the left elevator tab 10 a when the leftelevator 12 a rotates counter-clockwise relative to the left elevator 12a (or counter-clockwise about the left elevator rotational point 20 a),as illustrated in FIG. 4A.

Referring to FIG. 5B (in which the left horizontal stabilizer 14 a iseliminated for clarity), the left elevator tab 10 a may also rotateclockwise about the left tab rotation point 24 a. Such a clockwiserotation of the left elevator tab 10 a is involved in the “balance”function of the left elevator tab 10 a when the left elevator tab 10 arotates counter-clockwise relative to the left elevator 12 a (orcounter-clockwise about the left elevator rotational point 20 a), asillustrated in FIG. 4B. In addition, a clockwise rotation of the leftelevator tab 10 a is involved in the “anti-balance” function of the leftelevator tab 10 a when the left elevator tab 10 a rotates clockwiserelative to the left elevator 12 a (or clockwise about the left elevatorrotational point 20 a), as illustrated in FIG. 4B.

At this first time, the rotated or deployed left elevator tab 10 a (ineither “balance” or ‘anti-balance” mode) will have different aerodynamiccharacteristics that the right elevator 12 b and the right elevator tab10 b. Accordingly, the left elevator 12 a will be in a differentrelative position than the right elevator 12 b at the first time whenthe flight data is analyzed. Specifically, as illustrated in FIG. 6A(with the “anti-balance” configuration illustrated as an example only),the longitudinal axis 16 a of the left elevator 12 a (and thelongitudinal axis 18 a of the left elevator tab 10 a) extends through aleft reference axis 30 a at (or just prior to) the start time. At thefirst time, as illustrated in FIG. 6B, due to aerodynamic forces on theleft elevator tab 10 a, the longitudinal axis 16 a of the left elevator12 a makes an angle 32 a with the left reference axis 30 a at (or justprior to) the start time, and this position of the left elevator 12 amay be the first rotational position of the left elevator 12 a at thefirst time. The angle 32 a may be an acute angle that may be clockwiseor counter-clockwise, and the value of the angle may depend on manyvariables, such as airspeed and/or initial angle of the left elevator 12a relative to the left horizontal stabilizer 14 a, airspeed, forexample.

At the start time (illustrated in FIG. 6D) and at the first time(illustrated in FIG. 6E), and due to the intentional delay, the rightelevator tab 10 has not rotated relative to the right elevator 12 a.That is, at both the start time and at the first time, the longitudinalaxis 16 b of the right elevator 12 b (and the longitudinal axis 18 b ofthe right elevator tab 10 b) extends through a right reference axis 30 bthat is aligned with the left reference axis 30 a of the left elevator12 a, and this position of the right elevator 12 b may be the firstrotational position of the right elevator 12 b at the first time.

The right reference axis 30 b of the right elevator 12 b is aligned with(or corresponds to) the left reference axis 30 a of the left elevator 12a in space. That is, a plane may extend through or along each of theleft reference axis 30 a and the right reference axis 30 b, and theplane may be parallel to an axis or rotation of the left elevator 12 a(that extends through the left elevator rotational point 20 a of FIG.3A) and an axis or rotation of the right elevator 12 b (that extendsthrough the right elevator rotational point 20 b of FIG. 3A).

Accordingly, at the first time, the flight data may be analyzed tocompare the first rotational position of the left elevator 12 a(illustrated in FIG. 6B) to the first rotational position of the rightelevator 12 b (illustrated in FIG. 6E). This analysis of the flight data(as well as all analysis of flight data described in the followingsections) may be performed by the computer system 200 of FIG. 10, whichwill be described in more detail below. If the first rotational positionof the left elevator 12 a at the first time is different than the firstrotational position of the right elevator at the first time by at leasta first value or within a first range, an alert may be issued that theleft elevator tab 10 a is operating properly. For example, if the angle32 a between the left reference axis 30 a and the longitudinal axis 16 aof the left elevator 12 a is at a desired value or within a desiredrange (for example only, 0.5° to) 3.0° and the angle 32 b between theright reference axis 30 b and the longitudinal axis 16 b of the rightelevator 12 b is at a desired value or within a desired range (forexample only, 0.0° to) 0.4°, an alert may be issued that the leftelevator tab 10 a is operating properly. An example of proper operationof the left elevator tab 10 a between the start time and the first timecan be found in FIGS. 6A and 6B.

In addition, or alternatively, the flight data may be analyzed tocompare the first rotational position of the left elevator 12 a(illustrated in FIG. 6B) to the position of the first rotationalposition of the left elevator 12 a at or just prior to the start time(illustrated in FIG. 6A). If the first rotational position of the leftelevator 12 a at the first time is different than the rotationalposition of the left elevator 12 a at the start time by at least a firstvalue or within a first range, an alert may be issued that the leftelevator tab 10 a is operating properly. For example, if the angle 32 abetween the left reference axis 30 a and the longitudinal axis 16 a ofthe left elevator 12 a is at a desired value or within a desired range(for example only, 0.5° to) 3.0° at the first time, and the angle 32 abetween the left reference axis 30 a and the longitudinal axis 16 a ofthe left elevator 12 a is at a desired value or within a desired range(for example only, 0.0° to 0.4°) at the start time, an alert may beissued that the left elevator tab 10 a is operating properly.

As illustrated in FIGS. 7A to 7F, analysis of the flight data may showthat the left elevator tab 10 a is not functional. For example, ifanalysis of the flight data shows the first rotational position of theleft elevator 12 a at the first time is not different than (or is equalor approximately equal to) the first rotational position of the rightelevator 12 b at the first time, the first alert may be issued. Asanother example, if analysis of the flight data shows that the angle 32a between the left reference axis 30 a and the longitudinal axis 16 a ofthe left elevator 12 a is not at a desired value or within a desiredrange (for example only, 0.5° to 3.0°) at the first time (as illustratedin FIG. 7B) and/or if the difference in the angle 32 a at the first timeis not greater than a value or within a desired range (for example only,0.5° to 3.0°) then the angel 32 a at the start time (illustrated in 7A),then the first alert may be issued.

At the expiration of the intentional delay, which occurs at a secondtime, the right elevator tab 10 a rotationally displaces relative to theright elevator 12 a. The intentional delay may be any suitable length oftime between operation of the left elevator tab 10 a and the rightelevator tab 10 b. For example, the intentional delay may be 5 to 20seconds, for example. More specifically, the intentional delay may be 5to 20 seconds, or may be 10 seconds. If the intentional delay istriggered by the verification event that occurs at the start time, thesecond time is the value of the intentional delay.

Between the start time (and the first time) and just prior to the secondtime, the right elevator tab 10 b and the right elevator 12 b act as asingle control surface that rotates as a unit relative to a portion ofthe right horizontal stabilizer 14 b about a right elevator rotationalpoint 20 b, as illustrated in FIG. 3A. However, at the second time, theright elevator tab 10 b may rotatably displace in one of two directionsrelative to the right elevator 12 b (or relative to a point on the rightelevator 12 b). As illustrated in FIG. 5A (in which the right horizontalstabilizer 14 b is eliminated for clarity), the right elevator tab 10 amay rotate counter-clockwise about a right tab rotation point 24 b thatis disposed at or adjacent to a leading edge 26 b of the right elevatortab 10 b (and/or at or adjacent to a trailing edge 28 b of the rightelevator 12 b). Such a counter-clockwise rotation of the right elevatortab 10 b is involved in the “balance” function of the right elevator tab10 b when the right elevator tab 10 b rotates clockwise relative to theright elevator 12 a (or clockwise about the right elevator rotationalpoint 20 b), as illustrated in FIG. 4D. In addition, a counter-clockwiserotation of the right elevator tab 10 b is involved in the“anti-balance” function of the right elevator tab 10 b when the rightelevator 12 b rotates counter-clockwise relative to the right elevator12 b (or counter-clockwise about the right elevator rotational point 20b), as illustrated in FIG. 4A.

At or immediately after the expiration of the intentional delay (i.e.,at the second time), the right elevator tab 10 b makes (or finishedmaking) a displacement that corresponds to the displacement of the leftelevator tab 10 a. That is, the right elevator tab 10 b displaces (e.g.,rotationally displaces) in the same direction and to the same degree asthe left elevator tab 10 a (illustrated in FIGS. 4A to 4D), with theonly difference between the two being the timing of the start of therotational displacement. For example, if the left elevator 12 a isrotated counter-clockwise and the left elevator tab 10 a is in the“anti-balance” position of FIG. 4A, than the right elevator 12 b isrotated counter-clockwise (to the same degree as the left elevator 12 a)and the right elevator tab 10 b is in the “anti-balance” position ofFIG. 4A (to the same degree as the left elevator tab 10 a). Put anotherway, after the expiration of the intentional delay following theverification event, the left elevator 12 a and the left elevator tab 10a should have a cross-section that is identical or nearly identical tothe right elevator 12 b and the right elevator tab 10 b.

At this second time, the rotated or deployed right elevator tab 10 b (ineither “balance” or ‘anti-balance” mode) will have the same aerodynamiccharacteristics of the deployed left elevator tab 12 a (also in either“balance” or ‘anti-balance” mode). Accordingly, the right elevator 12 bwill move from the first rotational position of FIG. 6E into the same(or nearly the same) relative position as the left elevator 12 a at orslightly after the second time when the flight data is analyzed.Specifically, as illustrated in FIG. 6F (with the “balance”configuration illustrated as an example only), the longitudinal axis 16b of the right elevator 12 b makes an angle 32 b with the rightreference axis 30 b due to aerodynamic forces acting on the rightelevator tab 10 b, and this position of the right elevator 12 b may bethe second rotational position of the right elevator 12 b at the secondtime. Because the position of the left elevator tab 10 a and the leftelevator 12 a do not change from the first time to the second time, thesecond rotational position of the left elevator 12 a at the second timeis equal to or approximately equal to the first rotational position ofthe left elevator 12 a at the first time. That is, the angle 32 a doesnot change between the first time and the second time.

Consequently, at the second time, the flight data may be analyzed tocompare the first rotational position of the right elevator 12 b(illustrated in FIG. 6E) to the second rotational position of the rightelevator 12 b (illustrated in FIG. 6F). If the second rotationalposition of the right elevator 12 b at the second time is different thanthe first rotational position of the right elevator 12 b at the firsttime by at least a first value or within a first range, an alert may beissued that the right elevator 12 b is operating properly. For example,if the angle 32 b between the right reference axis 30 b and thelongitudinal axis 16 b of the right elevator 12 b is at a desired valueor within a desired range (for example only, 0.0° to 0.4°) at the firsttime, and if the angle 32 b between the right reference axis 30 b andthe longitudinal axis 16 b of the right elevator 12 b is at a desiredvalue or within a desired range (for example only, 0.5° to 3.0°) at thesecond time, an alert may be issued that the right elevator tab 10 a isoperating properly. An example of proper operation of the right elevatortab 10 a between the first time and the second time can be found inFIGS. 6E and 6F.

In addition (or alternatively), the flight data may be analyzed tocompare the second rotational position of the right elevator 12 b(illustrated in FIG. 6F) to the second rotational position of the leftelevator 12 a (illustrated in FIG. 6C). If the second rotationalposition of the right elevator 12 b at the second time is equal to (orapproximately equal to) or is the same as the second rotational positionof the left elevator 12 a at the second time (relative to the leftreference axis 30 a and the right reference axis 30 b), the rightelevator tab 10 b is functioning properly. An alert may then be issuedthat the right elevator tab 10 b is operating properly. For example, ifthe angle 32 b between the right reference axis 30 b and thelongitudinal axis 16 b of the right elevator 12 b is at a desired valueor within a desired range (for example only, 0.5° to 3.0°) at the secondtime, and if the angle 32 a between the left reference axis 30 a and thelongitudinal axis 16 a of the left elevator 12 a is at a desired valueor within a desired range (for example only, 0.5° to 3.0°) at the secondtime, an alert may be issued that the right elevator tab 10 a isoperating properly.

As illustrated in FIGS. 8A to 8F, analysis of the flight data may showthat the left elevator tab 10 a is functional but that the rightelevator tab 10 b is not functional. For example, at the second time,the flight data is analyzed to compare the first rotational position ofthe right elevator 12 b (illustrated in FIG. 8E) to the secondrotational position of the right elevator 12 b (illustrated in FIG. 8F).If the second rotational position of the right elevator 12 b at thesecond time is not different than (or is approximately equal to) thefirst rotational position of the right elevator 12 b at the first time,a second alert may be issued that the right elevator 12 b is notoperating properly. For example, if the angle 32 b between the rightreference axis 30 b and the longitudinal axis 16 b of the right elevator12 b is at a desired value or within a desired range (for example only,0.0° to 0.4°) at the first time, and if the angle 32 b between the rightreference axis 30 b and the longitudinal axis 16 b of the right elevator12 b is not at a desired value or within a desired range (for exampleonly, 0.5° to 3.0°) at the second time, the second alert may be issued.

In addition (or alternatively), the flight data may be analyzed tocompare the second rotational position of the right elevator 12 b(illustrated in FIG. 8F) to the second rotational position of the leftelevator 12 a (illustrated in FIG. 8C). If the second rotationalposition of the right elevator 12 b at the second time is not equal to(or approximately equal to) or within a range of (for example only, 0.0°to 0.4°) the second rotational position of the left elevator 12 a at thesecond time (relative to the left reference axis 30 a and the rightreference axis 30 b), the second alert may be issued. It may also bedesired that the angle 32 a between the left reference axis 30 a and thelongitudinal axis 16 a of the left elevator 12 a is at a desired valueor within a desired range (for example only, 0.5° to 3.0°) before thesecond alert is issued.

As illustrated in FIGS. 9A to 9F, analysis of the flight data may showthat the left elevator tab 10 a is not functional and that the rightelevator tab 10 b is not functional. For example, as a first determiningcondition, if analysis of the flight data shows the first rotationalposition of the left elevator 12 a at the first time (see FIG. 9B) isnot different than (or is equal or approximately equal to) the firstrotational position of the right elevator 12 b (see FIG. 9E) at thefirst time, then the left elevator tab 10 a is not functional. Inaddition, as a second determining condition, if analysis of the flightdata shows the second rotational position of the right elevator 12 a atthe first time (see FIG. 9F) is not different than (or is equal orapproximately equal to) the first rotational position of the rightelevator 12 b (see FIG. 9E) at the first time, then the right elevatortab 10 b is not functional. If both the first and second determiningcondition are satisfied, then the a third alert is issued, with thethird alert corresponding to a failure of both the left and rightelevator tabs 10 a, 10 b.

An alternative analysis of the flight data may show that the leftelevator tab 10 a is not functional and that the right elevator tab 10 bis not functional. For example, as a first determining condition, if thesecond rotational position of the left elevator 12 a at the second time(see FIG. 9C) is within a range (0.0 to 0.4°) of the initial rotationalposition of the left elevator at the start time (see FIG. 9C) and if thesecond rotational position of the right elevator 12 b at the second time(see FIG. 9F) is within the range (0.0 to 0.4°) of the initialrotational position of the right elevator 12 b at the start time (seeFIG. 9D), the third alert is issued a. The range is an angle 32 abetween the left reference axis 30 a and the longitudinal axis 16 a ofthe left elevator 12 a or an angle 32 b between the right reference axis30 b and the longitudinal axis 16 b of the right elevator 12 b.

The flight data may be analyzed and compared (and alerts may be issued)by any system or software (or combination of systems or software) knownin the art. For example, the flight data may be analyzed and compared byan algorithm, such as a filter placed within the recorded flight data.In some systems, a computing device may be employed, and the computingdevice may include a memory and a processor, with logic stored on thememory and executable by the processor.

The flight data may be analyzed for proper operation of the left andright elevator tabs 10 a, 10 b at any time, and such an analysis may beformed at any suitable time. For example, the flight data may beanalyzed for proper operation of the left and right elevator tabs 10 a,10 b after every flight of a particular aircraft, or periodically over asample of a fleet of aircraft.

In contemplated embodiments, the data may be analyzed in real time(either on board the aircraft and/or remote from the aircraft todetermine proper operation of the left and right elevator tabs 10 a, 10b. If either or both of the left and right elevator tabs 10 a, 10 b, aredetermined to be non-functional, a first, second, or third alert can beissued to the pilot, who can then take corrective action.

FIG. 10 illustrates a computer system 200 for assessing and verifyingoperation of elevator tabs. The computer system 200 accesses availablestored flight data 216, such as a flight data database implemented as aDigital Flight Data Recorder (“DFDR”), a quick access recorder (“QAR”)or other database, to assess operation of elevator tabs, in accordancewith the examples described herein. The system 200 may be implemented ina desktop computer, laptop computer, tablet computer, mobile device,smart-phone, network-enabled device, cloud based server, an applicationserver, a web server, etc. The computer system 200 may represent asingle one of these processing machines or a distributed combination ofsuch processing machines.

A signal-processing device 202 (or “signal processor” or “diagnosticdevice”) is coupled the stored flight data 216 through a wired orwireless communication network. The signal-processing device 202 mayhave a controller 204 operatively connected to a database 214 via a link222 connected to an input/output (I/O) circuit 212. It should be notedthat, while not shown, additional databases may be linked to thecontroller 204 in a known manner. The controller 204 includes a programmemory 206, one or more processors 208 (may be called microcontrollersor a microprocessors), a random-access memory (RAM) 210, and theinput/output (I/O) circuit 212, all of which are interconnected via anaddress/data bus 220. It should be appreciated that although only oneprocessor 208 is shown, the controller 204 may include multiplemicroprocessors 208. Similarly, the memory of the controller 204 mayinclude multiple RAMs 210 and multiple program memories 206. Althoughthe I/O circuit 212 is shown as a single block, it should be appreciatedthat the I/O circuit 212 may include a number of different types of I/Ocircuits. The RAM(s) 210 and the program memories 206 may be implementedas semiconductor memories, magnetically readable memories, and/oroptically readable memories, for example. A link 224, which may includeone or more wired and/or wireless (Bluetooth, WLAN, etc.) connections,may operatively connect the controller 204 to stored flight data 216through the I/O circuit 212. In some examples, a (pneumatic, electronic,optical, or some combination thereof) flight controller 225 is coupledto the stored flight data 216, through the link 224, to allow forautomated control of the operation of the elevator tabs in the event ofa fault condition or other operation automatically determined.

The program memory 206 and/or the RAM 210 may store various applications(i.e., machine readable instructions) for execution by the processor208. For example, an operating system may generally control theoperation of the signal-processing device 202 and provide a userinterface for the signal-processing device 202 to implement the stagesof the method 100 of FIG. 1. The program memory 206 and/or the RAM 210may also store a variety of subroutines 232 for accessing specificfunctions of the signal-processing device 202. By way of example, andwithout limitation, the subroutines 232 may include, among other things:a subroutine for determining an occurrence of a verification event thatincludes movement of a first elevator tab (e.g., a left elevator tab)relative to a first elevator (e.g., the left elevator) and a secondelevator tab (e.g., a right elevator tab) relative to a second elevator(e.g., a right elevator), wherein the verification event occurs at astart time, wherein the first elevator is at an initial rotationalposition and the second elevator is at an initial rotational position atthe start time; a subroutine for determining a first rotational positionof the first elevator at a first time and a first rotational position ofthe second elevator at the first time, the first time occurring afterthe start time; a subroutine for comparing the first rotational positionof the first elevator at the first time to the first rotational positionof the second elevator at the first time; a subroutine to issue a firstalert associated with the first elevator tab if the first rotationalposition of the first elevator at the first time is not different thanthe first rotational position of the second elevator at the first timeby at least a first value or by a first range; a subroutine to comparethe second rotational position of the first elevator at the second timeto the second rotational position of the second elevator at the elevatorat the second time; a subroutine to issue a second alert associated withthe second elevator tab if the second rotational position of the secondelevator at the second time is not within a second range of the secondrotational position of the first elevator at the second time; and asubroutine to determine that if (a) the second rotational position ofthe first elevator at the second time is within a third range of theinitial rotational position of the first elevator at the start time and(b) the second rotational position of the second elevator at the secondtime is within the third range of the initial rotational position of thesecond elevator at the start time, a third alert is issued associatedwith both the first elevator tab and the second elevator tab.

As previously explained, the subroutines 232 may include a subroutine togenerate an alert and/or alarm condition, for example, using the display226. That alert and/or alarm condition may be displayed as a web page,mobile device alert, tactile alert or alarm (e.g., via a vibratingfunction of a smartwatch or smartphone), or any other suitable visualand/or tactile (haptic) display. The subroutines 232 may communicatethis alert and/or alarm condition to a separate computing deviceconnected to the system 200 through a network connection. Such separatecomputing devices may include a server, laptop computer, handheldcomputer, monitor, mobile device such as a cellular phone orWi-Fi-enabled tablet, or other device. The subroutines 232 may include asubroutine to communicate the alert or other analysis thereof to aflight control system for operation of the elevators, elevator tabs, orother system to compensate for a detected fault condition. Thesubroutines 232 may also include other subroutines, for example,implementing software keyboard functionality, interfacing with otherhardware in the signal-processing device 202, etc. The subroutines 232may also include other subroutines, for example, implementing softwarekeyboard functionality, interfacing with other hardware in thesignal-processing device 202, etc. The program memory 206 and/or the RAM210 may further store data related to the configuration and/or operationof the signal-processing device 202, and/or related to the operation ofthe one or more subroutines 232. For example, the data may be datagathered by in the flight data 216, data determined and/or calculated bythe processor 208, etc. In addition to the controller 204, thesignal-processing device 202 may include other hardware resources. Thesignal-processing device 202 may also include various types ofinput/output hardware such as a visual display 226 and input device(s)228 (e.g., keypad, keyboard, etc.). In an embodiment, the display 226 istouch-sensitive, and may cooperate with a software keyboard routine asone of the software routines 232 to accept user input. It may beadvantageous for the signal-processing device 202 to communicate with abroader flight control systems (not shown) through any of a number ofknown networking devices and techniques.

The controller 204 may include any number of modules to analyze flightdata to verify proper operation of the left and right elevator tabs 10a, 10 b, and these modules may represent software code or hardware orstored instructions that implement the techniques described herein. Forexample, as illustrated in FIG. 11, the controller 204 may include aflight data module 302 that includes the aircraft's (or multipleaircrafts') flight data. The controller 204 may also include averification event detection module 304 that analyzes the flight data todetermine the occurrence of a verification event that includes movementof a first elevator tab (e.g., the left elevator tab 10 a) relative tothe first elevator (e.g., the left elevator 12 a) and the secondelevator tab (the right elevator tab 10 b) relative to the secondelevator (the right elevator 12 b). The verification event detectionmodule 304 may also determine an initial rotational position of thefirst elevator and an initial rotational position of the second elevatorat a start time, which is the time or point in time that theverification event occurred.

The controller 204 may additionally include a first rotational positionmodule 306 to analyze the flight data to determine a first rotationalposition of the first elevator at a first time and a first rotationalposition of the second elevator at the first time, the first timeoccurring after the start time.

The controller 204 may include a first comparison module 308 to comparethe first rotational position of the first elevator at the first time tothe first rotational position of the second elevator at the first time.

The controller 204 may include a first detection module 310 that issuesa first alert associated with the first elevator tab if the firstrotational position of the first elevator at the first time is notdifferent than the first rotational position of the second elevator atthe first time by at least a first value or by a first range. The firstdetection module 310 may also issue a first alert based on otherparameters described earlier to determine if the first elevator tab isfunctional.

The controller 204 may additionally include a second rotational positionmodule 312 to analyze the flight data to determine a second rotationalposition of the first elevator at a second time and a second rotationalposition of the second elevator at the second time. The second timeoccurs after the first time and the difference between the start timeand the second time being equal to an intentional delay betweenfunctionality of the first elevator tab and the second elevator tab.

The controller 204 may include a second comparison module 314 to comparethe second rotational position of the first elevator at the second timeto the second rotational position of the second elevator at the elevatorat the second time.

The controller 204 may include a second detection module 316 that issuesa second alert associated with the second elevator tab if the secondrotational position of the second elevator at the second time is notwithin a second range of the second rotational position of the firstelevator at the second time. The second detection module 316 may alsoissue a second alert based on other parameters described earlier todetermine if the second elevator tab is functional.

The controller 204 may include a third detection module 318 that issuesa third alert associated with both the first elevator tab and the secondelevator tab if (a) the second rotational position of the first elevatorat the second time is within a third range of the initial rotationalposition of the first elevator at the start time and (b) the secondrotational position of the second elevator at the second time is withinthe third range of the initial rotational position of the secondelevator at the start time. The third detection module 318 may alsoissue a third alert based on other parameters described earlier todetermine if both the first and second elevator tabs are functional.

The controller 204 may also include an optional corrective measuresflight data control interface module 320 that may initiate correctivemeasures based on the issuance of a first, second, and/or third alert.The corrective measures may provide information that identifies thefault and the aircraft, for example. The corrective measures may also bein-flight instructions or relating to the first, second, and/or thirdalert.

The controller 204 may analyze the flight data after a flight hasoccurred or may perform real-time analysis of flight data. Although themodules 312-320 are represented as discrete, independent modules in FIG.11, a single module (or multiple modules) could perform any of thefunctionalities associated with any of the modules provided in FIG. 11.

While various embodiments have been described above, this disclosure isnot intended to be limited thereto. Variations can be made to thedisclosed embodiments that are still within the scope of the appendedclaims. For example, the first elevator tab may be the right elevatortab disposed at an end portion of the first elevator, which is the rightelevator of the aircraft. Correspondingly, the second elevator tab maybe the left elevator tab disposed at an end portion of the secondelevator, which may be the left elevator of the aircraft.

What is claimed is:
 1. A method of verification of proper operation of afirst elevator tab disposed at an end portion of a first elevator of anaircraft and a second elevator tab disposed at an end portion of asecond elevator of the aircraft, the method comprising: determine theoccurrence of a verification event that includes movement of the firstelevator tab relative to the first elevator and the second elevator tabrelative to the second elevator, wherein the verification event occursat a start time, wherein the first elevator is at an initial rotationalposition and the second elevator is at an initial rotational position atthe start time; determine a first rotational position of the firstelevator at a first time and a first rotational position of the secondelevator at the first time, the first time occurring after the starttime; compare the first rotational position of the first elevator at thefirst time to the first rotational position of the second elevator atthe first time; if the first rotational position of the first elevatorat the first time is not different than the first rotational position ofthe second elevator at the first time by at least a first value or by afirst range, issue a first alert associated with the first elevator tab;determine a second rotational position of the first elevator at a secondtime and a second rotational position of the second elevator at thesecond time, the second time occurring after the first time and thedifference between the start time and the second time being equal to anintentional delay between functionality of the first elevator tab andthe second elevator tab; compare the second rotational position of thefirst elevator at the second time to the second rotational position ofthe second elevator at the elevator at the second time; if the secondrotational position of the second elevator at the second time is notwithin a second range of the second rotational position of the firstelevator at the second time, issue a second alert associated with thesecond elevator tab; and if (a) the second rotational position of thefirst elevator at the second time is within a third range of the initialrotational position of the first elevator at the start time and (b) thesecond rotational position of the second elevator at the second time iswithin the third range of the initial rotational position of the secondelevator at the start time, issue a third alert associated with both thefirst elevator tab and the second elevator tab.
 2. The method of claim1, wherein the first elevator is a left elevator and the first elevatortab is a left elevator tab, and the second elevator is a right elevatorand the second elevator tab is a right elevator tab.
 3. The method ofclaim 1, wherein the intentional delay is between 6 and 20 seconds. 4.The method of claim 3, wherein the intentional delay is between 8 and 14seconds.
 5. The method of claim 1, wherein the verification event ismoving the aircraft's flap handle out of an “up” detent.
 6. The methodof claim 1, wherein the verification event is a detection of a failureof one or both of the primary and secondary hydraulic systems of theaircraft.
 7. The method of claim 1, wherein the first range is betweenabout 0.5° and about 3.0°.
 8. The method of claim 1, wherein the secondrange is between about 0.0° and about 0.4°.
 9. The method of claim 1,wherein the third range is between about 0.0° and about 0.4°.
 10. Asystem to analyze flight data to verify proper operation of a firstelevator tab disposed at an end portion of a first elevator of anaircraft and a second elevator tab disposed at an end portion of asecond elevator of the aircraft, the system comprising a computingdevice including a memory and a processor, the memory adapted to storenon-transitory computer executable instructions, wherein thenon-transitory computer executable instructions, when executed by theprocessor, cause the system to: analyze the flight data to determine theoccurrence of a verification event that includes movement of the firstelevator tab relative to the first elevator and the second elevator tabrelative to the second elevator, wherein the verification event occursat a start time, wherein the first elevator is at an initial rotationalposition and the second elevator is at an initial rotational position atthe start time; analyze the flight data to determine a first rotationalposition of the first elevator at a first time and a first rotationalposition of the second elevator at the first time, the first timeoccurring after the start time; compare the first rotational position ofthe first elevator at the first time to the first rotational position ofthe second elevator at the first time; wherein if the first rotationalposition of the first elevator at the first time is not different thanthe first rotational position of the second elevator at the first timeby at least a first value or by a first range, issue a first alertassociated with the first elevator tab; analyze the flight date todetermine a second rotational position of the first elevator at a secondtime and a second rotational position of the second elevator at thesecond time, the second time occurring after the first time and thedifference between the start time and the second time being equal to anintentional delay between functionality of the first elevator tab andthe second elevator tab; compare the second rotational position of thefirst elevator at the second time to the second rotational position ofthe second elevator at the elevator at the second time; wherein if thesecond rotational position of the second elevator at the second time isnot within a second range of the second rotational position of the firstelevator at the second time, issue a second alert associated with thesecond elevator tab; and wherein if (a) the second rotational positionof the first elevator at the second time is within a third range of theinitial rotational position of the first elevator at the start time and(b) the second rotational position of the second elevator at the secondtime is within the third range of the initial rotational position of thesecond elevator at the start time, issue a third alert associated withboth the first elevator tab and the second elevator tab.
 11. The systemof claim 10, wherein the first elevator is a left elevator and the firstelevator tab is a left elevator tab, and the second elevator is a rightelevator and the second elevator tab is a right elevator tab.
 12. Thesystem of claim 10, wherein the intentional delay is between 6 and 20seconds.
 13. The system of claim 12, wherein the intentional delay isbetween 8 and 14 seconds.
 14. The system of claim 10, wherein theverification event is moving the aircraft's flap handle out of an “up”detent.
 15. The system of claim 10, wherein the verification event is adetection of a failure of one or both of the primary and secondaryhydraulic systems of the aircraft.
 16. The system of claim 10, whereinthe first range is between about 0.5° and about 3.0°.
 17. The system ofclaim 10, wherein the second range is between about 0.0° and about 0.4°.18. The system of claim 10, wherein the third range is between about0.0° and about 0.4°.